In recent years, thin-shaped image display devices have been practically used which are constituted by using thin-shaped image display panels such as liquid crystal display panels, plasma image display panel, EL (electroluminescent) image display panels, etc. as image display elements.
These image display devices contain electric circuits in which heat is generated for example from integrated circuits including output-stage transistors, semiconductors, resistors, and transformers. That is, heat is generated intensively from electronic components with great electric power of electrothermal conversion. Along with high definition or ultra-high definition, a recent image display device has risen in drive frequency at which display signals are supplied to a large number of pixels of the panel. For this reason, in particular, there has been an unignorably large increase in self-heating of an integrated circuit driving the source lines of a display device.
Patent Literature 1 discloses a technique for, in order to reduce the chip size of an integrated circuit, wiring a power supply without drawing inner power wires to power pads surrounding a chip. FIG. 5 shows a schematic view of the layout of a liquid crystal driver (source driver). FIG. 5 is a diagram showing the arrangement of output cells and power wires in the liquid crystal driver, which is an integrated circuit.
The liquid crystal driver has a large number of output cells 101 arranged for driving source lines of liquid crystals. Further, each of the output cells 101 has, as its components, a latch circuit 102, a level shifter 103, a DAC circuit 104, an operational amplifier 105, and a pad 106, for example.
The latch circuit 102 retains data in accordance with which a display is carried out. The level shifter 103 shifts the latched data to a liquid crystal driving power supply level. The DAC circuit 104 outputs a drive voltage corresponding to the data. The operational amplifier 105 makes an impedance conversion of the voltage outputted from the DAC circuit 104 and outputs the voltage. The pad 106 connects the integrated circuit, i.e., the liquid crystal driver, to wires of a package. Each of the output cells 101 has its components linearly arranged as shown in FIG. 5.
Since the components of each of the output cells 101 need to be supplied with electric power, the integrated circuit has power pads 108 disposed therearound. In the case of such disposition of the power pads 108, as shown in FIG. 5, it is necessary to lead wires from the output cells 101 to the power pads 108. In FIG. 5, two power pads 108 are provided to which the operational amplifiers 105 are connected through a wire 109a. Similarly, the DAC circuits 104 are connected to the power pads 108 through a wire 109b, and the level shifters 103 are connected to the power pads 108 through a wire 109c. A power supply for the latch circuits 102 is separate from the power pads 108, and as such, is not described here. In this way, each type of component is supplied with electric power through a separate wire. Such wiring prevents noise attributed to the operation of one type of component from affecting another type of component.
FIG. 6 shows the shape of a film package in which a liquid crystal driver has been mounted. The liquid crystal driver shown in FIG. 6 is a liquid crystal driver 113 mounted on a film package substrate 110. The film package has an output terminal 111 formed in such a way as to extend along one long side of the film package substrate 110, and has an input terminal 112 formed in such a way as to extend along the other long side of the film package substrate 110. The input terminal 112 includes package power terminals connected to the power pads 108 of the liquid crystal driver 113 through wires 114, respectively. FIG. 6 omits to illustrate other input and output wires.
The lead wires 109a to 109c shown in FIG. 5 need to be low in resistance, and as such, need to be great in line width. In particular, the wire 109a for the operational amplifier section generates big switching noise because it is necessary to charge and discharge capacitive loads such as the pixels of a liquid crystal panel through the wire 109a. For this reason, it is necessary to connect the operational amplifier section to the power supply through a low-resistance power wire.
FIG. 7 is a diagram of bypassing of a power wire using the technique of Patent Literature 1. As shown in FIG. 7, a bypass wire 201 provided on a tape substrate and a power supply line 109a for the operational amplifiers are connected to each other through bumps 202 disposed on the power supply line 109a. 
FIG. 8 shows the state of a film package in which a liquid crystal driver has been mounted. The film package of FIG. 8 has a bypass wire 201 added as a wire on the film package substrate 110 in addition to the components of FIG. 6. The bypass wire 201 has bumps 202 provided for use in the power wire for the operational amplifiers. The bypass wire 201 is connected to the same power input terminals of the input terminal 112 as the power wires 114.
The foregoing configuration can reduce the resistance of the wires to the power supply from the power pads to the operational amplifier section of the output cells, and as such, can quickly absorb switching noise.